1. Field of the Invention
This invention relates generally to wireless communication systems. More particularly, it relates to a method and system for adapting a wireless communication system to provide a desired functionality and to optimize economic benefit by varying one or more of a number of components or processing techniques.
2. Description of the Related Art
Recently, the market for wireless communications has enjoyed tremendous growth. Wireless technology now reaches or is capable of reaching virtually every location on the face of the earth. Hundreds of millions of people exchange information every day using pagers, cellular telephones and other wireless communication products.
With the appearance of inexpensive, high-performance products based on the IEEE 802.11a/b/g Wireless Fidelity (Wi-Fi) standard, acceptance of wireless local area networks (WLANs) for home, Small Office Home Office (SOHO) and enterprise applications has increased significantly. IEEE 802.11b/g is a standard for a wireless, radio-based system. It operates in the unlicensed 2.4 GHz band at speeds up to 11 M bits/sec for IEEE 802.11b and 54 M bits/sec for IEEE 802.11g. The IEEE 802.11b/g specification sets up 11 channels within the 2.4 GHz to 2.4835 GHz frequency band which is the unlicensed band for industrial, scientific and medical (ISM) applications. IEEE 802.11a is another standard for a wireless, radio-based system in the ISM band. It operates in the unlicensed 5-GHz band at speeds up to 54 M bits/sec.
It has been found that WLANs often fall short of the expected operating range when actually deployed. For example, although a wireless Access Point (AP) is specified by a vendor as having an operating range of 300 feet, the actual operating range can vary widely depending on the operating environment.
In particular, WLAN performance can be greatly degraded by direct and multipath radio interference. Multipath occurs in wireless environments because the radio frequency (RF) signal transmitted by the subscriber is reflected from physical objects present in the environment such as buildings. As a result, it undergoes multiple reflections, refractions, diffusions and attenuations. The base station receives a sum of the distorted versions of the signal (collectively called multipath).
Similarly, in any indoor wireless system, multipath interference effects occur when the transmitted signal is reflected from objects such as walls, furniture, and other indoor objects. As a result of multipath, the signal can have multiple copies of itself, all of which arrive at the receiver at different moments in time. Thus, from the receiver's point of view, it receives multiple copies of the same signal with many different signal strengths or powers and propagation delays. The resultant combined signal can have significant fluctuation in power. This phenomenon is called fading.
Unlike all other parts of the radio spectrum, a license is not required to operate a transmitter in the ISM bands specified in IEEE 802.11a/b/g. In exchange for this license-free environment, users implementing the IEEE 802.11b/g and IEEE 802.11a standards are subject to interference from other users of the bands. The 2.4 to 2.4835 GHz ISM band is particularly sensitive to interference because it is populated with numerous wireless networking products such as Bluetooth systems, HomeRF systems, IEEE 802.11b WLAN devices, microwave ovens, and cordless phones that can result in significant interference. This interference is the result of a myriad of incompatible data transmission techniques, uncoordinated usage of spectrum, and over-subscription of the available spectrum.
Many devices operating in the 2.4 to 2.4835 GHz ISM band can either be classified as direct sequence spread spectrum (DSSS) or frequency hopping spread spectrum (FHSS) systems. The DSSS data transmission scheme is used primarily by IEEE 802.11b systems. FHSS systems, such as Bluetooth devices, differ from DSSS systems in their implementation for avoiding interference. FHSS systems avoid interference with other transmission signals in the same band by hopping over many different frequency channels. To provide FHSS systems with more bandwidth, the United States Federal Government Federal Communications Commission (FCC) has allowed FHSS systems to operate at wider bandwidths. The operation of FHSS systems at wider bandwidths has the potential to increase interference between DSSS and FHSS products. The interference level of narrowband FHSS systems on DSSS transmission has already been found to be severe.
There are additional elements of performance degradation in a network of 802.11b/g WLAN access points (APs). Since the 802.11b/g channel bandwidth is approximately 16 MHz, only three non-overlapping channels operating in proximity can be accommodated without interfering with one another. The channel re-use factor imposes a severe restriction on implementation of 802.11b/g based systems which requires significantly more effort in the network deployment, and increases the chances of interference and packet collision especially within an environment with a dense user cluster, such as in an office building.
Several approaches for improving the operating performance and range in a fading environment have been suggested. In one conventional approach, selection antenna diversity is used to reduce the effect of multipath fading. Multiple antennas are located in different locations or employ different polarizations. As long as the antennas have adequate separation in space or have a different polarization, the signal arriving at different antennas experiences independent fading. Combining (or selection) is performed at a dedicated receiver for an antenna or at a receiver used for multiple antennas to improve the quality of received signals. Each antenna can have a dedicated receiver or multiple antennas can share the same receiver.
In another conventional approach, signal combining is used to provide improved performance in a fading environment. Signal combining techniques employ multiple spatially separated and/or orthogonally polarized antennas. The received signal is obtained by combining the signals from the multiple antennas. One technique for providing optimal signal quality is known as maximal ratio combining (MRC). Another combining technique that maximizes the output signal-to-interference-plus-noise ratio is known as minimum mean square error (MMSE) combining.
The signals can be combined in the combining techniques based on a weighting scheme. Weights used in combining techniques can be generated with blind and non-blind techniques. In non-blind techniques, the received signal is demodulated and data sequences in the received signal are used to determine the portion that is the desired signal and the portion that is noise and interference. The demodulated signal is used to determine the combining weights through correlation with the received signals. In blind techniques, a property of the signal is used to distinguish it from interference and noise. In one approach, a constant modulus algorithm (CMA) is used to take advantage of a signal property of a constant signal envelope in order to generate a set of antenna weights such that the constant envelope property can be maintained. Signal combining techniques typically achieve better performance than the selection diversity antenna approaches at the expense of added implementation complexity.
Another known approach to achieve performance improvement is through equalization, either in the time or frequency domain. In this technique, the multipaths arriving at the receiver are delayed, phase shifted, and amplitude scaled before they are combined (equalized).
U.S. Pat. No. 6,167,283 describes optimization of selection of a cell in a cellular radio system where there are available cells of different capabilities and/or where the capability of a terminal to make use of different services of the cells varies from one terminal to another. For example, the cells can provide different services based on the maximum bit rate offered by the base station. A prediction is produced about what kind of service level will be needed in the next connection between a terminal and a base station. A cell is selected such that the service level offered by the base station corresponds to the prediction produced by the terminal.
U.S. Pat. No. 6,134,453 describes an omni-modal wireless product which is adaptive to the selectively variable desires of the end user. The product is capable of utilizing any one of wireless data services within a given geographical area based on a user defined criteria. The user defined criteria can include the cost of sending a data message using the wireless communication network, the quality of transmission link in the wireless communication network (signal strength, interference actual or potential), the potential for being dropped by the wireless communication system, and the security of wireless communication network. An adaptive control circuit is used for determining which wireless communications networks are available at a given location and time, for accessing a selected wireless communication network, for communicating with the selected wireless communication network to determine on a real time basis the operating characteristics of the wireless communication network, and for generating a frequency control signal and a protocol control signal in response to the user defined criteria to cause the device to communicate with the selected wireless communication network using the frequencies and modulation protocol suitable for transmission of the signal information over the selected wireless communications network. The frequency control signal and the protocol control signal are generated by comparing operating characteristics of the selected wireless communication network with the user defined criteria.
U.S. Pat. No. 6,246,870 describes a method for controlling expense incurred by a communications terminal that communicates with a first mobile radio-telephone communications system and a second mobile radio-telephone communication system by selecting the radio-telephone communication system which provides economic efficiencies in a particular mode of operation. More specifically, expenses incurred by a communications terminal that communicates with a first mobile radiotelephone system and a second mobile radiotelephone system are controlled by storing first and second critical values which characterize a tariff structure of the respective first and second mobile radiotelephone communication systems. Communications units used by the communications terminal are measured. An economic efficiency associated with use of the terminal to communicate with the first and second mobile radiotelephone communications systems is determined from the measured communications units and the first and second stored critical values. Measures are initiated to control communications usage with the first and second radiotelephone communications systems by the terminal based on the determined economic efficiency.
While some of the above-described patents have been concerned with optimization of a wireless network system based on selection of a wireless network providing certain characteristics, none of the above-described patents are concerned with optimization of economic value to an end user by altering the complexity of the wireless network system based on the end user's desires.
It is desirable to provide a wireless communication system that can be adaptively configured to provide performance selected by the end user while providing an optimization of an economic benefit to the end user, such as one or more of range extension, multipath mitigation and interference suppression.